1. Field of the Invention
The present invention relates to a solid-state imaging device and a manufacturing method of the same, electronic equipment, and a semiconductor device, and specifically, to a solid-state imaging device in which pixels having photodiodes are arranged in a matrix on a light receiving surface and a manufacturing method of the same, electronic equipment including the solid-state imaging device, and a semiconductor device.
2. Background Art
In a solid-state imaging element represented by a CCD and a CMOS image sensor used for an area sensor, a photoelectric conversion part of photodiodes, a wiring part that transmits generated signals, transistors, etc. are formed on a semiconductor substrate. The element has a structure in which an on-chip lenses are formed on the photoelectric conversion part, and incident light is collected to the photoelectric conversion part by the on-chip lenses and photoelectrically converted.
Recently, in the solid-state imaging elements, demands for higher resolution and more pixels have been increasing. In the situation, to obtain higher resolution without increasing chip sizes, it is necessary to reduce the area per unit pixel for higher integration.
However, if the area per unit pixel is reduced, the amount of light entering the photodiode forming the photoelectric conversion part is not sufficient. Especially, in a CMOS image sensor, a distance from the on-chip lens to the photodiode region is longer due to its multilayer wiring structure. Accordingly, light entering obliquely does not reach the photodiode region but enters an adjacent photodiode, and not only reduction in sensitivity but also color mixing and lower resolution are caused.
In order to solve the problems, JP-A-11-121725 and JP-2000-150845 disclose a structure in which an optical waveguide formed by surrounding a core material with a high refractive index using a cladding material with a low refractive index between the photodiode and the on chip lens is provided.
To take an incidence angle as the optical waveguide, it is preferable to take a difference between refractive indices of the cladding material with the low refractive index and the core material with the high refractive index as large as possible. For example, a silicon oxide film with a refractive index of 1.5 or less is widely used for the cladding part (low-refractive-index part) of the optical waveguide structure formed on the photodiodes. On the other hand, for the core part (high-refractive-index part), an inorganic film of silicon nitride or diamond-like carbon (DLC) having a high refractive index, or an organic film of a siloxane resin or a polyimide resin is being studied. JP-2007-119744 and JP-2008-166677 disclose solid-state imaging devices using the above mentioned materials.
As an optical waveguide material, siloxane resin is being studied. The siloxane resin has a structure in which, to a skeleton of alternately bound silicon and oxygen, methyl groups and phenyl groups are bound as side chains. The siloxane resin has an extremely high filling characteristic for a minute hole, and may have both a high refractive index and heat resistance if a component that does not form a conjugated system but has aromaticity is introduced into the component of the siloxane.
As the optical waveguide material for coating, all materials that have refractive indices of 1.55 or more at a wavelength of 550 nm and are soluble in an organic solvent of γ-butyrolactone or cyclohexanone can be used. Further, by dispersing fine particle having a high refractive index and a size sufficiently smaller than that of visible light, for example, fine particles of zirconia or titania of 80 nm or less in siloxane, much higher refractive index can be reached without absorption of light.
When the siloxane resin is used as a material of the core part of the optical waveguide, the siloxane is formed on the entire surface of a wafer by coating. Accordingly, a dicing region (scribing part) is also covered by a siloxane film.
The subsequent steps will be explained with reference to the drawings.
For example, as shown in FIG. 15A, pixels are formed in a pixel area A1 of a semiconductor substrate 110 having a wafer shape. In each pixel, for example, a transistor including a photodiode 111, a diffusion layer 112, and the like, a multilayer insulating film 115 including an interlayer insulator film 113, a contact plug 114, and silicon oxide, a wiring layer 116 including copper, etc. are formed. The multilayer insulating film 115 is provided with a recessed part for optical waveguide 118, a protector film 117 of silicon nitride or the like is formed to cover the inner walls thereof, and a first light transmission layer 151 of siloxane resin or the like is formed to fill the region inside thereof. The first light transmission layer 151 forms a core part 151a with a high refractive index within the recessed part for optical waveguide 118. In the layer on the first light transmission layer 151, color filters 152 of blue (B), green (G) or red (R) are formed with respect to each pixel. In the layer on the color filters, on-chip lenses 153a are formed with respect to each pixel. The on-chip lenses 153a are formed by a light transmissive material, and a second light transmission layer 153 of the material is formed on the entire surface of the wafer. On the first light transmission layer, a transparent planarization layer that transmits light for improvement of adhesion to the color filters may be formed on the entire surface of the wafer.
In a logic area A2 of the semiconductor substrate 110, transistors including diffusion layers 121 and the like, multilayer insulating films 123 including contact plugs 122 and silicon oxide, wiring layers 124 including copper, etc. are formed. A protector film 117 is formed on the entire surface of them. In a pad area A3 of the semiconductor substrate 110, a pad electrode 131 is formed, and the protector film 117 is formed on the entire surface thereof. The protector film 117 in the part on the pad electrode 131 is removed for externally connectable configuration.
In a guard ring area A4 of the semiconductor substrate 110, a guard ring G as a structure including a multilayer insulating film 141, a conducting layer 142 having the same layers as those of the wiring layers 124 of copper or the like, a conducting layer 143 having the same layers as those of the pad electrode, etc. is formed. The guard ring G is provided at an end of one semiconductor chip. An area between two guard rings G is a dicing area A5. As described above, since the first light transmission layer 151 is formed on the entire wafer surface, the dicing area A5 is formed to be covered by the layer. Further, on the first light transmission layer 151, the second light transmission layer 153 as the on-chip lenses 153a in the pixel area A1 is stacked. In the configuration, in the pad area A3, a pad opening PO is formed to reach the pad electrode 131. At the following steps, as shown in FIG. 15B, dicing D is performed in the dicing area 5A using a dicing blade or the like to form separate pieces for each chip.
Here, in the siloxane resin, the main chain easily polarizes and shows polarity because silicon has lower electronegativity than oxygen. On the other hand, the methyl groups of the side chains are hard to polarize and shows non-polarity. Generally, the outer side of siloxane is covered by methyl groups having non-polarity and the like and shows water/oil repellency, and has poor adhesion to other materials. Further, when the siloxane film is heated and hardened for three-dimensional cross-linkage to increase its strength, the siloxane film becomes brittle. The siloxane in which inorganic nanoparticles are put for raising the refractive index is especially brittle, and a crack easily occurs. The siloxane film has low adhesion to the upper and lower films as described above, and is brittle and the crack easily progresses. Accordingly, when the siloxane film exists in the dicing area, as shown in FIG. 15B, a crack C occurs in the siloxane film due to mechanical stress and impact force of the dicing blade rotating at a high speed during dicing. Starting from the crack C, peeling easily occurs at the interface between the siloxane film and the upper film and the interface between the siloxane film and the lower film in poor adhesion. If the peeling of the films progresses from the scribing part to the pixel part, image quality becomes deteriorated.
Further, when chippings produced by dicing are attached onto the on-chip lenses in the pixel area, light does not reach the photodiodes in the part with the chippings thereon and the output signal level becomes lower, and these lead to deterioration in image quality. When the siloxane resin is used as the material of the core part of the optical waveguide as described above, peeling occurs at the interface between the siloxane and the upper layer or the lower layer during dicing and reaches the pixel area, chippings produced by dicing are attached to the pixel area, and thereby, deterioration in image quality and yield is caused.